Examples of laundry machines generally includes a washing machine having only a washing function of washing clothing, and a machine having both washing and drying functions. The washing machine having only a washing function is a product that removes various contaminants from clothing and bedding using the softening effect of a detergent, friction of water streams and shock applied to the laundry to according to rotation of a pulsator or a drum. A recently introduced automatic washing machine automatically performs a series of operations including a washing operation, a rinsing operation and a spin-drying operation, without requiring user intervention.
The laundry machine capable of drying clothes is a type of laundry machines that has not only the function of the washing machine dedicated to washing but also the function of drying the laundry after washing.
Laundry machines capable of drying laundry supply high-temperature air (hot air) to the laundry, and can be classified into an exhaust type and a circulation (or condensation) type depending on how air flows through the machine.
The exhaust type laundry machine supplies heated air to the laundry accommodating part, but discharges the air coming out of the laundry accommodating part from the laundry machine instead of circulating the air.
The circulation type laundry machine circulates air in a laundry accommodating part storing the laundry by removing moisture from the air (i.e., dehumidifying the air) discharged from the laundry accommodating part, heating the air, and then resupplying the air to the accommodation part.
Hereinafter, a conventional circulation type laundry machine having the drying function will be briefly described with reference to FIG. 1. As shown in FIG. 1, the circulation type laundry machine 1 having the drying function 1 includes a cabinet 10 provided with an introduction port 12 defining an accommodation space therein and allowing laundry to be introduced therethrough and an a door 14 to open and close the introduction port 12, a tub 20 to accommodate the cabinet 10, a drum 40 rotatably installed in the tub 20 to accommodate laundry to be dried, and an air supply unit 50 to supply the drying air to the tub 20 to dry the laundry.
Herein, the air supply unit 50 includes a condensation duct 51 formed at the exterior of the tub 20 to condense the air containing moisture produced in the tube 20, a heating duct 54 connected to the downstream side of the condensation duct 51 in the flow direction of the air to heat the air through a heater 56 and to supply the heated air into the tub, and an air-blowing fan 53 causing the air in the tub 20 to circulate along the condensation duct 51 and the heating duct 54.
In drying the laundry in the laundry machine 1 configured as above, the air moved by the air-blowing fan 53 is heated by the heater 56 provided to the heating duct 54, and the heated air is supplied into the tub 20. Thereby, the laundry is dried by rotation of the drum 40 and the hot air. Thereafter, the heated air having dried the laundry changes to humid air as the laundry is dried. The humid air flows from the tub 20 into the condensation duct 51, and the moisture is removed from the air in the condensation duct 51.
Herein, separate cooling water is supplied to the condensation duct 51 to condense the humid air. The air introduced into the condensation duct 51 is supplied back to the heating duct 54 by the air-blowing fan 53, thereby circulating through the process described above.
The condensation duct 51 is formed in the shape of a pipe in consideration of the volumetric capacity of the air-blowing fan 53 and smooth air flow, and the inner surface of the condensation duct 51 condenses moisture contained in the humid air through exchange of heat with the humid air to remove the moisture from the air. To condense the moisture in the humid air introduced into the condensation duct 51, a large amount of cooling water needs to be consistently supplied during the laundry drying process.
Meanwhile, the air supply unit 50 provided to the conventional laundry machine having the function of drying includes an air-blowing fan 53 to discharge the air from the laundry accommodating part and a heating duct 54 to heat the air caused to flow by the air-blowing fan 53.
That is, in the conventional laundry machine 1, the air-blowing fan 53 is positioned before the heating duct 54 with respect to the air flow direction, and thus the air flowing out of the laundry accommodation part (i.e., the tub 20) sequentially passes through the air-blowing fan 53 and heating duct 54, and is then supplied back to the laundry accommodation part.
The conventional laundry machine as described above uses a heater which is configured to heat the air to supply high temperature air (hot air) to the laundry.
Such heaters include a gas heater to burn a gas to heat the air and an electric heater to heat the air through electric resistance. Recently, the electric heater is widely used as it is easily installable and has a simple structure.
However, when the air is heated by the electric heater, the high-temperature heat of the heater may be directly transferred to the laundry, damaging the laundry and even leading to fire in the laundry machine.
In addition, since the electric heater heats the air using electricity, heating the air to a desired temperature may consume a large amount of electricity, thereby increasing maintenance expenses.
Moreover, removing moisture from the air having dried the laundry disadvantageously requires injection of a large amount of cooling water into the condensation duct.
In this regard, a laundry machine capable of generating hot air through a heat pump having an evaporator, a compressor, a condenser and an expander through which a refrigerant circulates, and an air blower has recently been developed and is increasingly widely used.
In the case of such laundry machine with a heat pump, the evaporator may remove moisture contained in the air, and the condenser may heat the air and supply and circulate the heated air to the tub to dry the laundry.
That is, a typical heat pump has a circulation cycle in which a refrigerant supplied from the compressor condenses moisture contained in the air and heats the air through heat exchange occurring in the evaporator and the condenser, and then returns to the compressor.
The circulation cycle of the refrigerant may be smoothly implemented by the compressor only when heat exchange consistently occurs in the evaporator and the condenser during the circulation cycle. That is, for the laundry machine having the function of drying and employing a heat pump, it is important to maintain constant heat exchange during operation of the heat pump.
However, when the drying cycle is performed in the laundry machine having the function of drying and employing the heat pump, the heat pump may overheat. That is, at the initial start and final start of the heat pump, heat exchange in the evaporator or the condenser is not balanced with that in the condenser or the evaporator, and thus the discharge pressure of the compressor increases, overloading the compressor.
In this case, the operational temperature of the heat pump excessively increases, and the pressure of the refrigerant discharged from the compressor excessively increase. Thereby, the efficiency of the heat pump may not be normally exhibited.